Engines may use various forms of fuel delivery to provide a desired amount of fuel for combustion in each cylinder. One type of fuel delivery uses a port injector for each cylinder to deliver fuel to respective cylinders. Still another type of fuel delivery uses a direct injector for each cylinder.
Further, engines have been proposed using more than one type of fuel injection. For example, the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. are one example. Specifically, the Heywood et al. papers describes directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. The ethanol provides increased charge cooling due to its increased heat capacity compared with gasoline, thereby reducing knock limits on boosting and/or compression ratio. In this way, improved engine fuel economy may be achieved.
However, the inventors herein have recognized several issues with such an approach. Specifically, distribution of separate fuels for a vehicle may require significant infrastructure changes, and in some locations, both fuels may not be available.
Thus, in one approach, the above issues may be addressed by using a system for an engine. The system comprises: a cylinder located in the engine; a first injector configured to inject gasoline fuel into said cylinder; a second injector configured to inject a fluid into said cylinder, said fluid containing at least some water.
By using a fluid with at least some water, such as pure water or a water-ethanol blend, it is possible to enable operation under increased compression ratio and/or increased boosting while reducing knock issues even if the second fuel is not always available, or only limited amounts are available.
In another approach, a method for controlling an engine may be provided, the method comprising: injecting a fuel into a combustion chamber of the engine via a first injector; injecting fluid containing water into said combustion chamber via a second injector; and varying an amount of water injection as operating conditions vary to improve engine performance.
By varying an amount of water injection via the second injector, it is possible to provide charge cooling only when needed to avoid or reduce engine knock and thereby achieve improved efficiency. Further by utilizing a separate injector, it is possible to maintain acceptable performance, injector size, injector targeting, etc., for injected fuel, while still enabling water injection.
In still another approach, a method for controlling an engine may be used, the method comprising: injecting a fuel into a combustion chamber of the engine via first injector; injecting a fluid containing water into said combustion chamber via a second injector; and varying an amount of injection of said fluid as an amount of water in said fluid varies.
In this way, it is possible to account for a varying charge cooling effect of the injected fluid. Further, by enabling varying of water content in the fluid, it is possible to take advantage of water blends, such as water and ethanol blends, for example.